A Study of the Tomography and Seismicity in Taipei Basin and Tatun Volcano Regions, Taiwan and Their Structural Implications
Date Issued
2009
Date
2009
Author(s)
Lin, Yu-Mei
Abstract
The Taipei Basin with ‘soft’ deposit in the north of Taiwan has been produced by the motion of the Shanchiao fault. To the north, Tatun Volcano Group (TVG) which has post-volcanic activities is located adjacent to Taipei Basin. The local seismicity in Taipei Basin is very low. On the contrary, there are quite a few micro-earthquakes being detected in TVG. Therefore, it is very important to understand the seismotectonics of the Taipei Basin and TVG.n this research, in order to increase ray path coverage and improve the resolution, I picked the seismic arrival times and combined the earthquake catalogs from two local temporary seismic networks located in Taipei and Tatun region, the Central Weather Bureau Seismic Network (CWBSN) and the Taiwan Strong Motion Instrumentation Program (TSMIP) to establish a new seismic tomography image. Totally, 6861 events detected at more than 7 stations during periods from 1979 to 2007 were used to determine Vp and Vp/Vs structures as well as focal mechanisms.n our tomography results, the pattern of low Vp/Vs ratio in this region seems to coincide with the Shanchiao fault, and the region with high Vp/Vs ratio above it reveals that the effects of basin amplification affects about several kilometers. Besides, the shallow region with low Vp/Vs and high Vp beneath TVG should represent the solidified igneous rocks.he hypocenter distribution of micro-earthquakes beneath TVG can be classified into two groups. These two seismogenic zones at the shallow portion are coincident with the surface hydrothermal regions with hot spring and fumaroles. Those regions include Chishing Mountain, Matsao and Tayukeng. The focal mechanisms of those earthquakes are normal fault types with strike-slip component by using P wave first motions and these solutions have various strikes and dips even the events are close in time and spatial windows. This phenomenon is commonly observed in a volcanic area. Thus, those earthquakes may reflect the broken zone and unobstructed conduits exist beneath the TVG and the gas and liquid can pass through. o, based on the hypocenter distribution and focal mechanism solutions, it seems that these earthquakes are weakly correlated with the nearest fault - Chinshan fault. Besides, these two seismogenic zones incline to different directions and may imply that they are different passageways for the hydrothermal fluid and gas to ascend along from different sources.
Subjects
tomography
Tatun Volcano Group
Taipei Basin
Type
thesis
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